1. Field of the Invention
The present invention relates to an encoder for use in, for example, displacement sensors.
2. Description of the Related Art
An encoder generates periodic signals that differ in phase. The periodic signals output from the encoder and different in phase are input to a processing circuit, which counts cycles per unit time. The processing circuit can acquire data from the periodic signals input to it. The data represents, for example, the direction of movement, position, displacement and speed of a moving body.
Jpn. Pat. Appln. KOKAI Publication No. 2001-56238 discloses an encoder shown in FIG. 10. As shown in FIG. 10, the encoder has an original-signal generating means 1. The means 1 generates three pseudo sine-wave signals CA, CB and −CA that differ in phase by 90° from one another. The pseudo sine-wave signals CA, CB and −CA are input to a sine-wave-signal generating means 2. The means 2 performs an operation, or resistance division, on the signals CA, CB and −CA, generating pseudo sine-wave signals d0 to d7. The signals d0 to d7 pass through an impedance adjusting means 5 and are converted to signals d0′ to d7′. These signals d0′ to d7′ are supplied to a comparing means 3. The comparing means 3 performs digitalization on the signals d0′ to d7′, generating digitalized signals D0 to D7. The digitalized signals D0 to D7 are supplied to an interpolation circuit 4. The interpolation circuit 4 generates two-phase encoder digital signals A and B from the digitalized signals D0 to D7. The signals A and B differ in phase by 90°.
Jpn. Pat. Appln. KOKAI Publication No. 2001-56238 teaches the technique of supplying three pseudo sine-wave signals CA, CB and −CA directly to a sine-wave signal generating means 2. It is desired that the pseudo sine-wave signals CA, CB and −CA be at the same reference potential. If so, the means 2 can generate, from the signals CA, CB and −CA, pseudo sine-wave signals d0 to d7 that accord with a specific resistance ratio. Namely, the pseudo sine-wave signals d0 to d7 generated by the sine-wave signal generating means 2 are at phase intervals set by the resistance ratio. If the resistance ratio of such a value that the signals d0 to d7 are at regular phase intervals, the signals d0 to d7 will be at regular intervals at the same reference voltage. Thus, the interpolation circuit 4 can perform interpolation at high precision.